I just read a really interesting book: Selfish Reasons to Have More Kids: Why Being a Great Parent is Less Work and More Fun Than You Think. In it, economist Bryan Caplan argues that tacking an extra kid onto your current family size is almost always a good thing—and he does it all with numbers.

If you’ll indulge me to present a bit of Caplan’s argument: the main thrust is that parents actually have very little long-term effect on their children’s habits, character, and temperaments. In short, no matter how good a parent one might be, he says, the “nature” factor of progeny plays a huge role in determining what lies in store for various individuals. Caplan offers a series of twin and adoption studies to this effect—showing that identical twins in different environments turn out to be remarkably similar, even after decades apart.

This is counterintuitive, he admits—and we with children are doubtless the first to agree! But the numbers do present some compelling evidence in favor of “nature” over “nurture”—at least in terms of long-term outcomes. (In the short-run, parental influence is much more palpable; but it’s not surprising that most of this wears off in time.)

Caplan uses all of this to make the claim that, since most kids turn out “alright” in the end—given the forces of “nature” and the high general probability of becoming a functional adult—parents don’t need to work themselves to death (read: spend 40+ hours per week on childcare) just to see their kids live fulfilling lives. And since most of the “benefits” of having kids come later in life—e.g., grandchildren, etc.—another kid or two now seems a pretty good investment to make in order to see a long return in 40 or so years.

Whether or not you buy Caplan’s logic is up to you. (In fairness, you should read the book to get a better, clearer picture before deciding either way.)

Regardless, one thing Caplan’s argument can’t do is speak to the moral character of family planning. Even if, in terms of a “return on investment” model, my having an extra child now becomes “profitable” in the mid- to long-range future, the economic perspective is, unfortunately, quite blind to the values inherent in persons at the most basic level. (This is the case even if we consider “profitability” very charitably, e.g., as “contributing to my personal fulfillment and well-being, and also the well-being of all society.”)

This plays out in pretty distinct ways. For example, after arguing strongly (and with surprising force) that more kids are usually better than less, the question comes up as to how to treat artificial methods of procreation. After all, according to Caplan, life is a “gift”—and because it’s inherently good, making life possible seems to be a good thing in itself. What’s to hold us back, then, from pursuing artificial insemination, IVF, or even pre-implantation genetic selection in getting the best possible life around?

From the moral perspective, this is where things break down. Rating the pros and cons of having another kid from an economic viewpoint is great—assessing the “risk profile,” so to speak. But dealing well with living human beings is another matter entirely from dealing with their creation. The first can plausibly fall under the banner of economics; but the second is distinctly ethical (i.e., philosophical).

Caplan’s book can teach us a few things. First of all, it’s a helpful reminder that parenting is supposed to be a joyful, fulfilling, and beneficial experience. The name of the game isn’t to run yourself ragged. Rather, it’s to raise children who come to understand the value of hard work, but also the joy of leisure and the beauty of personal interactions. The economic arguments succeed in this regard; and they’re quite compelling.

But the book also reminds us that people—those that work, relax, and interact—aren’t at bottom quantifiable entities. Quite the contrary, they’re the beings whose ultimate good is benefitted by proper quantification, production, and equilibrium. In a word, people aren’t the subject of good economics; instead, they ought always to be the beneficiaries of economics done well.

Whether or not to have another child is a decision that entails quite a few factors—financial, psychological, and moral, alike. But the one thing we cannot do is separate out these factors from one another in an attempt to oversimplify the question. Family planning is, in the end, a fairly involved reality. In a word, it’s more than just numbers. And it will do us, and our future children well to remember that.

Andrew Haines is president of the Center for Morality in Public Lifeand a PhD student in Philosophy at The Catholic University of America. He lives in Virginia with his wife, Kathleen, and their son.